I thought that it was time to start a new thread devoted to the JUNO Jupiter Orbiter mission. This New Frontiers Mission #2 seems to be a "stealth" project with little information available on the Web. In fact, the official NASA JUNO web site is quite pitiful. It contains the minimal amount of information on what seems to be an intriguing mission, in terms of both science and engineering.

Does the UMSF community have information on this mission that has not been widely seen before?

Or just turn to that address for the overall JPL Technical Papers site and type in "juno" in the search window. (This same technique works for lots of other interesting JPL papers, too.)

I have a few crumbs more information about this mission besides those in the article, which I'll reprint here as soon as I get over this damn headache. One thing we had better purge purselves of, though, is the hope that it will do any significant studies of the Galilean moons. It's designed to study Jupiter -- period -- and its orbit and mission duration make it almost impossible for it to study anything else (except for long-range studies of Io's ionosphere and torus).

OK, here are those crumbs. The JPL description is pretty good, but there are a few things missing from it:

(1) The 2002 Solar System Decadal Survey noted that the five main goals for the next Jupiter mission are: (A) Determine if Jupiter has a central core to constrain models of its formation; ( B ) determine the planetary water abundance; ( C ) determine if the winds persist into Jupiter's interior or are confined to the weather layer; (D) assess the structure of Jupiter's magnetic field to learn how the internal dynamo works; and (E) measure the polar magnetosphere to understand its rotation and relation to the aurora. Juno will do a nice job on all five - and while, the Survey's original desire for at least one and preferably 2 or 3 deep entry probes (down to 100 bars) would have further improved the data on ( B ) and ( C ), the added expense was so great that a deep Jovian Multiprobe Flyby mission by itself is now ranked pretty low on the list of desired New Horizons missions -- shallow Galileo-type entry probes of the other giant planets are higher-ranked. Moreover, the data from Juno will allow us to better plan the targeting of those deep Jupiter entry probes when we finally DO fly them. (Note also that -- if they absolutely have to descope Juno -- they could toss off every single instrument except the microwave radiometer and magnetometer, and lose only goal (E) in the process.)

(2) Currently we know Jupiter's gravity-field harmonics down to level 6 -- Juno will take it down to level 12 to 14. Not only can it nail down the size of any hevy-element core -- which is crucial to decide which of the two rival theories of giant-planet formation is true -- but it can measure that core's rotation rate, and even obtain profiles of the density of the planet's middle layers sensitive enough to determine how deep its convective wind cycles really run, all the way down 1/5 of the way to the core!

(3) Our current knowledge of Jupiter's magnetic-field harmonics is level 4. Juno will take it all the way down to level 20 -- much BETTER than we can ever obtain for Earth itself, where we're forever limited to level 14 due to interference from crustal fields! Thus Juno is likely to provide radical new information not only on the generative processes of Jupiter's magnetic field (including the dynamo radius and changes with time), but of Earth's field as well.

(4) Knowledge of the total oxygen content of Jupiter's atmosphere is crucial -- and the Galileo entry proe didn't get it because of its bad-luck fall (9-1 odds against) into a hot spot where a downdraft removed the local water vapor. The probe DID find not only that the concentration of the other heavier elements -- Ar, Kr, Xe, C, N and S -- was somewhat lower than expected, but that they were very consistent in being enriched about threefold relative to the Sun, whereas much bigger element-to-element differences had been expected in that ratio. This was a shock. The logical conclusion is that the icy planetesimals that formed Jupiter were actually made of much colder ice than that which existed at the planet's current distance from the Sun (150 K) -- those other elements were imprisoned either in regular ice at only 20-30 deg K or clathrates at >38 K, so either the planet itself formed much farther from the Sun and migrated a great distance inwards, or the planetesimals that formed it themselves came from much farther out and migrated inwards before accreting to form Jupiter at something like its present distance from the Sun. (The entry probe found further confirmation of this in the nitrogen isotopic ratios, which indicates that Jupiter's nitrogen was originally delivered as molecular N rather than as ammonia -- which in turn provides an odd clash that I've mentioned elsewhere with the indications from Huygens that Titan's nitrogen DID arrive as ammonia in relatively warm ice.)

Since water ice was the carrier of all these other heavier elements, we need to know the ratio of water ice to them -- for which we must know Jupiter's current oxygen content. If the planet's oxygen is enriched to only about the same degree relative to the Sun as all the other heavier elements measured by the Galileo entry probe, then they must have been carried into the planet in very cold water ice, from the Kuiper Belt or beyond -- and Jupiter itself may have originally accreted at that distance and then spiralled a great distance inwards. But if oxygen turns out to be enriched more relative to its solar abundance than those other elements -- say, about 9 times solar abundance -- then those other elements were trapped by water ice, and carried into the forming Jupiter, in a more diluted form as clathrate ices, which could have formed somewhat closer to the Sun.

The microwave radiometer (whose viewfield is 1 degree at the equator and 4 degrees at the poles) should allow water abundance measurements down to about 100 bars -- plus better ammonia data (which is a bit fuzzier from the Galileo probe than we would like), thus nailing down both Jupiter's overall oxygen content, and further sharpen our data on its nitrogen content. It will also get more data on the temperature and cloud depth profiles in different parts of the planet, which in turn should help tell us more about just how deep the convective and wind patterns that create the belt-zone structures really run. But it can only do all this reliably because the Galileo entry probe measured the other trace components of Jupiter's atmosphere -- some of which, like PH3, have a significant effect on the planet's microwave spectrum.

(5) Juno's mission is scheduled to run 32 orbits of 11 days each -- and any extended mission will be only a month or so, because they want to make sure that they can crash it into Jupiter, and thus avoid any chance of contaminating Europa, before they lose control of it from radiation damage. In fact, they may end the mission ahead of time -- most of its science will come from its first 16 orbits, and its periapsis latitudes are designed to give it only 5% of its total radiation dosage during that period. (As the JPL paper says, 5 of its first 7 orbits are directed toward microwave radiometry, with all the rest of its orbits being devoted to precision tracking for gravity-field data.)

(6) Juno spins at 3 rpm. Its "JunoCam" -- the most dispensable of all its instruments, whose data will be processed by students at JPL -- should send back 5-10 images per orbit. Juno is focused entirely on the planet itself -- any data it does get on the moons will be pure gravy. For instance, it's very unlikely that they will be able to arrange for it to fly through Io's flux tube.

Using solar power for JUNO has always intrigued me. Starting with Pioneer 10 and onward all of our outerplante probes (including the ESA Ulysses) have been nuclear powered. The stated reason is that the available sunlight gets too low much beyond the orbit of Mars or the mid-asteroid belt.

Yet here is JUNO using solar. The panels in the diagram don't look all that much bigger big to me in relation to the craft than say the Viking orbiters or MRO, yet the solar power at Jupiter must be less than 1/4 what it is at Mars.

What am I missing? Are they using amazingly compact and low powered instruments? Is a large percentage of the power being used to charge batteries much of the time, then the batteries are used for peak power usage?

Using solar power for JUNO has always intrigued me. Starting with Pioneer 10 and onward all of our outerplante probes (including the ESA Ulysses) have been nuclear powered. The stated reason is that the available sunlight gets too low much beyond the orbit of Mars or the mid-asteroid belt.

Yet here is JUNO using solar. The panels in the diagram don't look all that much bigger big to me in relation to the craft than say the Viking orbiters or MRO, yet the solar power at Jupiter must be less than 1/4 what it is at Mars.

What am I missing? Are they using amazingly compact and low powered instruments? Is a large percentage of the power being used to charge batteries much of the time, then the batteries are used for peak power usage?

The panels actually ARE somewhat bigger than those for the Mars missions. Solar panels actually are feasible to power Jupiter craft, IF you stay out of the intense radiation regions (which took a lot of careful orbital planning for Juno), which will quickly fry them -- and if you're willing to accept their weight. All three of the Discovery proposals which were Juno's ancestors (two of which were orbiters, and one of which was a finalist twice) used lightweight solar arrays -- and, in fact, the suggestion was made to put FOUR such solar panels on a copy of one of those craft and use it as the flyby carrier for a Saturn entry probe! http://www.lpi.usra.edu/meetings/outerplan...01/pdf/4113.pdf

By the way, ESA's Rosetta comet craft, which has big solar panels, has an aphelion all the way out at Jupiter's orbit -- but it will be in a state of near-hibernation during those periods.

QUOTE (Bart @ Apr 11 2006, 01:09 AM)

I was rooting around on the ADS server, looking for papers related to Juno, and I found this one.

It describes an instrument for Juno, but it's not one that's mentioned in the mission overview linked above. Is it a recent addition, a pipe dream, or something in between?

Bart

I'm about to look into this. Apparently it may be added to the payload, but I haven't heard anything from any other source about it. If they can squeeze it on (maybe as a replacement for the JunoCam), it could be very useful.

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